Personally i think the ideal 5 animal pack for me would be something like:
Moose/Elk: We need more deer and northern ungulate species in general and both would be a welcome addition to fill that niche. Personally i dont really care which one, but from the general perception of the community the Moose is the more wanted animal.
Turkey: I feel like the Turkey isnt talked about enough in these forums. In my book it would be an ideal addition, especally in a small dlc, just for the diversity and flexibility it brings. It is a small bird, thats like nothing we have in the game (you could say peacock, but these guys, especally the males are some bulky imposing badboys), that would work both as a wild habitat animal, in aviaries as a ground dweller and as a farm animal. Criminally underrated if you ask me, especally compared to just another bear, big cat or crocadilian
Aligator and/or Blackbear/Cougar: Speaking of them, i still feel like atleast one of these three should defenetly be part of the pack, maybe even two if one of them is the aligator. They are just to iconic to be left out completly, but they dont feel as needed and wouldnt bring as much new (yes the aligator is a reptile, but a reptile house with 4 diffrent flavours of crock doesnt have to be bad, but i think you see the point)
The 4th pick would be the fun pick! I dont really care about the specific animal, but i want it to be a small animal like a mustelid or racoon. Wolverines, fish- and seaotters, skunks, badgers or just a standard marten would all be a great addition and i would be happy with any of them!